Distribution transformer

ABSTRACT

POLE MOUNTED DRY-TYPE DISTRIBUTION TRANSFORMER HAVING A CAST EPOXY COIL. THE COIL AND ITS ASSOCIATED CORE STRUCTURE ARE MOUNTED IN AN L-SHAPED FRAME MEMBER AND SECURED IN PLACE BY A STRAP MEMBER. THE L-SHAPED FRAME MEMBER FURNISHES THE SUPPORTING MEANS FOR ATTACHING THE CORE AND COIL TO A UTILITY POLE. A POLYGONALLY SHAPED PROTECTIVE HOUSING ENCLOSES THE FRAME AND THE COIL AND CORE ASSEMBLY. THE LOW VOLTAGE BUSHINGS ARE ATTACHED TO THE BOTTOM PORTION OF THE PROTECTIVE HOUSING ADJACENT TO LOUVRES WHICH AID IN COOLING THE TRANSFORMER.

Feb. 20, 19:73 J,F' COTTQN I I 3,717,832.

uisrnmumou TRANSFORMER Filed Aug. 2. 1971 lllllll [H III IHIHM United States Patent Olhce 3,717,832 DISTRIBUTION TRANSFORMER John F. Cotton, Athens, Ga., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa. Filed Aug. 2, 1971, Ser. No. 167,938 Int. Cl. H01f 15/02, 27/06 US. Cl. 33667 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention This invention relates, in general, to electrical inductive apparatus, and, more specifically, to pole mounted dry-type distribution transformers.

Description of the prior art The majority of pole mounted distribution transformers in use at the present time use oil as the liquid coolant. There are some inherent disadvantages in using oil filled transformers which are mounted on utility poles. Such transformers can be considered hazardous since some failures of oil filled transformers have resulted in ignition of the oil, explosions and consequential damage to the area near the transformers. The weight of the oil filled transformer hampers installation of the unit on the utility pole. To overcome these disadvantages, a considerable amount of eflfort has been expended by the industry in developing an air cooled distribution transformer suitable for utility pole mounting.

Most of the dry-type distribution transformers known in the prior art have mounting arrangements which are similar to conventional oil filled transformer arangements, however, the insulation systems are modified to withstand the high operating temperatures encountered. The core and coil assembly is mounted in an end frame for the purpose of securing the laminations and the position of the coil. The unit is then placed in and attached to a casing which usually has a cylindrical shape. The casing serves as a weather safety protector around the core and coil assembly and also provides the mounting means for attaching the transformer to a utility pole.

The feasibility of dry-type distribution transformers have been improved by the recent developments in cast epoxy coils which may withstand high operating temperatures. To realize the full benefits of a dry-type distribution transformer, it is desirable to eliminate the structures which are used with oil filled transformers and which are unnecessary in dry-type transformers. Therefore, it is an object of this invention to provide a dry-type pole mounted distribution transformer which does not use the conventional tank and casing structures which have been associated with oil filled transformers and some drytype transformers.

SUMMARY OF THE INVENTION The new and useful distribution transformer disclosed herein uses the magnetic core assembly as part of the overall structural assembly used for supporting itself. The

3,717,832 Patented Feb. 20, 1973 2 transformer is supported directly by the frame which secures the core and coil assembly, rather than being supported by the protective housing.

The magnetic core is positioned in an L-shaped frame with a strap extending between the ends of the frame and positioned over the core assembly. A wound magnetic core and a cast epoxy coil are used so that the core and coil assembly is capable of withstanding the forces exerted by the other structural supporting members. The L-shaped frame is attached directly to the utility pole or another type of transformer supporting structure. The protective housing is attached to the frame and may be made of a suitable lightweight material, including insulating materials, since it is used for protection rather than support. The apparatus disclosed by this invention provides a compact, lightweight and safe dry-type transformer for use in power distribution systems.

BRIEF DESCRIPTION OF THE DRAWING Further advantages and uses of this invention will become more apparent when considered in view of the following detailed description and drawing, in which:

FIG. 1 is a side elevational view of a distribution transformer constructed according to this invention with the protective housing removed;

FIG. 2 is a static force diagram illustrating some forces which may occur in the transformer supporting assembly;

FIG. 3 is a front elevational view of the distribution transformer shown in FIG. 1 with the protective housing removed; and

FIG. 4 is a view of a distribution transformer constructed according to this invention with the protective housing attached.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description similar reference characters refer to similar members in all figures of the drawing.

Referring now to the drawing, and FIG. 1 in particular, there is shown a side elevational view of a distribution transformer with the protective housing removed. A coil 10, which is enclosed in a cast epoxy weatherproof bushing, is disposed in inductive relationship with the wound magnetic core 12. The coil 10 includes a high voltage lead 14 which is connected to one side of the primary winding within the casting. The core and coil assembly 16 is mounted in an L-shaped frame which may be constructed from a U-shaped metal channel. The side portions of the U-shaped channel extend around the magnetic core 12 at the bottom position 20 and at the side positions 22 and 24. A retaining means, such as the strap 26, is attached to the frame 18 by the bolts 28 at the upper portion of the frame and by the bolts 30 at the outer portion of the frame. The strap 26 secures the core and coil assembly 16 in the frame 18 and gives the outer portion of the frame 18 addition-a1 support.

The mounting brackets 32 and 34 are attached to the frame 18 by a suitable process, such as welding, and are used to mount the transformer onto its supporting structure. The transformer is shown in FIG. I mounted onto a utility pole 40 by the bolt-nut means 36 and 38. Although shown mounted onto a utility pole. It is within the contemplation of this invention that the transformer may be mounted onto another type of supporting structure.

FIG. 2 is a static force diagram which illustrates some of the forces which may act on the core and its supporting assembly, indicating the balanced relationship obtainable by using the magnetic core as part of the overall supporting means. Without a supporting structure such as the strap 26 shown in FIG. 1, the weight of the core and coil assembly may produce a force on the outer portion of the supporting frame which tends to bend the frame. By attaching a strap between the upper and outer portions of the frame and placing it over the upper outside corner of the wound core, the bending forces are relocated.

The vector 42 represents the strap force at the upper outside corner of the core which acts toward the outer portion of the frame. The vector 44 represents the strap force which acts toward the upper portion of the frame. The vector 46 represents the resulting force represented by the vectors 42 and 44. Since the vector 46 has a com ponent in the horizontal direction, the force vectors 48 and 50 represent the force exerted by the upper portion of the frame against the magnetic core to counteract the force from the strap 26. This produces frictional forces which act vertically to help support the core and coil assembly 16. The vertical force on the magnetic core which counteracts the force from the strap 26 is indicated by the vector 52. The unique construction of Wound magnetic cores makes them especially suitable for transmitting forces without the need for core braces. Therefore, the strap 26 provides additional support for the outer portion of the frame 18 and the weight force of the core and coil assembly 16 is counteracted to some extent by the vertically acting frictional forces.

FIG. 3 is a front elevational view of the distribution transformer shown in FIG. 1, which is also mounted on a utility pole 40. The L-shaped frame 18 is only slightly wider than the thickness of the magnetic core 12. The magnetic core 12 fits between the side portions 54 of the U-shaped channel from which the frame 18 is constructed. The cast coil extends from the core windows beyond the frame 18. The low voltage of secondary leads 56 extend from the casting for connection to the secondary bushings. The primary lead 58 is usually connected to a member which will be at ground potential, such as the strap 26.

A complete distribution transformer constructed ac cording to this invention and including a protective housing is illustrated in FIG. 4. The transformer is shown mounted onto a utility pole 40. The protective housing has a substantially octagonal shape in the vertical plane and a substantially rectangular shape in the horizontal plane. The octagonal shape provides a flat surface near the coil leads for mounting the bushings. Since the protective housing does not support the heavy core assembly, it may be constructed from a lightweight material. It must have enough strength to shield the core and coil assembly from the weather and prevent accidental contact with inner parts of the transformer. The protective housing may be constructed of a metallic material, a fiber glass reinforced plastic material, or any other suitable material. The embodiment illustrated uses a top cover 62 which is riveted to the side portions of the protective housing 60. The high voltage bushing 64 may be attached to the top cover 62 as illustrated or at another location on the protective housing. The low voltage bushings 66 and 68 may be attached near the bottom of the protective housing 60, as shown, for convenience in connecting the secondary lines. This location arrangement of the low voltage bushings has not been used extensively with oil filled distribution transformers due to the problems associated with oil leaks around the openings in the housing for the bushings. Ventilation areas, such as the louvres or grills 70, may be used to aid in the circulation of the air within the housing 60. Ventilation areas may also be used at other positions on the housing, such as the side 71, to permit air to flow through the housing. Molding the low voltage bushings 66 and 68 as part of the protective housing 60 is possible,

especially if the housing is constructed from a reinforced plastic material.

The novel apparatus disclosed herein utilizes the core and coil assembly as a structural element in the supporting assembly to provide a highly compact, lightweight, safe and reliable pole-type distribution transformer. Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all of the matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative rather than limiting.

I claim as my invention:

1. Transformer apparatus suitable for mounting on a support structure, said transformer apparatus comprising a magnetic core, a coil assembly, and an L-shaped frame member having an upper end and an outer end, said magnetic core and coil assembly being disposed on said frame member, a strap connected to the upper and outer ends of said frame member and positioned over said magnetic core for retaining said core and said coil assembly in position on said frame member, said strap being positioned and constructed to utilize said magnetic core and coil assembly as a structural supporting element, said frame member having means thereon for attaching said transformer to the support structure.

2. The transformer apparatus of claim 1 wherein said coil assembly is cast in a resin housing, and the L-shaped frame member is constructed from U-shaped channel members with sides of the channel members enclosing part of the magnetic core.

3. The transformer apparatus of claim 1 including a protective housing which is disposed around and supported by the frame member, said protective housing being polygonally shaped in a vertical plane and rectan- I gularly shaped in a horizontal plane, with low voltage bushings protruding from the lower half of the housing.

4. The transformer apparatus of claim 1 including a protective housing which is disposed around the frame member, said protective housing being constructed from an insulating material.

5. The transformer apparatus of claim 4 wherein the protective housing is constructed from a reinforced plastic material.

6. The transformer apparatus of claim 4 wherein the low voltage bushings are constructed as an integral part and of the same material as the protective housing.

References Cited UNITED STATES PATENTS 2,148,449 2/1939 Edwards 336-67 3,262,078 7/ 1966 Foerster 33667 3,321,168 5/1967 DEntremont 336- 2,816,947 12/1957 Leightner 3.3690 2,699,531 11/1955 Massar 336-67 X 3,544,938 12/ 1970 Bengmann et a1. 33692 3,617,966 11/1971 Trench et al. 33692 FOREIGN PATENTS 6405560 11/1965 Netherlands 3'3667 THOMAS J. KOZMA, Primary Examiner U.S. Cl. X.R. 

